Abstract: β-Blockers in food of animal origin was determined by liquid chromatography-tandem mass spectrometry（LC-MS/MS）. According to the mathematic model, the uncertainty sources of test results were analyzed, such as the standard solution preparation, sample weighing, regression equation, method repeatability. Each component uncertainty was calculated through analyzing. With the limits of quantification of 0.5 μg/kg for all analytes, the expanded uncertainty was calculated while the combined standard uncertainty of β-blockers residue was obtained. Comparing of each component of uncertainty in the process, the results show that the effect of the least squares fitting is the maximun.